DESCRIPTION (After the Application): Suboptimal choice of medications for primary care is a significant source of prescribing errors that can compromise patient safety. Prescribing calcium channel blockers for hypertension, for example, instead of firstline, evidence-based agents such as diuretics and beta blockers, is a prescribing error that can lead not only to higher costs of medical care but also to higher rates of morbidity and mortality. An educational intervention to reduce prescribing errors in hypertension could therefore result in improved patient outcomes and patient safety. In 1995, Harvard Community Health Plan (HCHP), a large HMO in New England, began an internally-funded, pilot educational program that implemented three different strategies to reduce primary care physicians? errors in prescribing antihypertensive medications. These interventions, carried out as a randomized controlled trial in three managed care settings (2 different staff-model divisions of the HMO, and a group-model division of the HMO), were 1) mailed dissemination of educational materials (control); 2) mailed dissemination plus group academic detailing, and 3) mailed dissemination plus individual academic detailing. The study population comprised approximately 5,000 hypertensive patients who received care from 104 primary care physicians. For purposes of later evaluation, this program randomly assigned three comparable group practices, one in each of three HCHP divisions (nine total physician groups) to one of three experimental groups (control, group detailing, individual detailing). This application describes a comprehensive evaluation of the educational program by collecting, merging, validating, and analyzing data from ambulatory encounters, outpatient claims, and pharmacy dispensing databases from the three divisions of HCHP to measure the effects of the study interventions on reducing prescribing errors in hypertension. The principal analyses will examine the immediate and long-term effects of the educational interventions on 1) incident prescribing of sub-optimal agents; and 2) switching from sub-optimal agents to first-line agents. This study will also analyze the program costs and medication cost savings. Dissemination will capitalize on collaboration with AHRQ, and the HMO Research Network?s Center for Education and Research on Therapeutics (CERT).